Insurance against medical expenses and loss of earnings due to accident or illness. This may cover individuals only, or extend to their dependants. Health insurance schemes may be compulsory or voluntary, and their cost may fall on individuals or on their employers. Compulsory schemes can cover any form of health risk. Voluntary schemes typically charge premiums related to members’ apparent risk, depending on factors such as age, sex, and occupation. A voluntary scheme which did not charge premiums related to apparent risk for members would be subject to adverse selection: it would attract people with high risks, and would therefore need to charge high premiums. These would make it unattractive to people who appeared to be better risks, who would find that they could get cheaper cover from more selective schemes. Voluntary schemes also often exclude the cost of treatment for conditions that members are known to have when they first join. Health insurance may also exclude risks believed to be under a member’s own control, for example pregnancy.